Between 10% and 20% of patients with hypercortisolism (Cushing's syndrome) have ectopic production of adrenocorticotropin hormone (ACTH). In approximately 50% of these patients, the source of ACTH cannot be found despite very detailed and extensive examination including imaging studies such as computed tomography scanning, magnetic resonance imaging, and octreotide scan using the conventional low dose of 111-indium pentetreotide ([111In-DTPA-D-Phe]-pentetreotide). This protocol tests whether [18F]-fluorodeoxyglucose (FDG) positron emission tomography (PET) scanning or use of a higher dose of [111In-DTPA-D-Phe]-pentetreotide can be used to localize successfully the source of ectopic ACTH production. To date fluorodeoxyglucose PET scanning successfully identified the tumor in less than 30% of patients.Low dose Octreoscan successfully localized the tumor in more than 40% of patients. High dose Octreoscan successfully localized the tumor in only one patient out of seven patients in whom low dose Octreoscan was negative. This study continues to find out whether fluorodeoxyglucose PET scanning and high dose Octreoscan compared to conventional imaging modalities can provide additional imaging strategies for patients with ectopic Cushing's syndrome.